In a prior art, a wet cleaning method using a chemical solvent has been mainly employed to clean a surface of a semiconductor wafer or mask. In the conventional wet cleaning method, sulfuric acid (H2S04), hydrochloric acid (HCl), ammonia (NH4OH), peroxide (H2O2), hydrogen fluoride (HF) and the like, as the solvent, is used to be mixed with water. In addition to the solvent, a technology using an ultrasonic or megasonic wave in a wet cleaning process has been known.
However, the above wet cleaning method has been faced with problems of environmental pollution caused by use of a large quantity of chemical, a slow operating speed, a requirement for a massive cleaning apparatus, complicated and inferior working conditions and the like. Accordingly, study on a dry cleaning method substituting for the above wet cleaning method having the above problems has been conducted actively in the art.
As such a dry cleaning method, a technology for removing contaminants on a surface of a workpiece, in particular a semiconductor or mask, with laser has been known. However, the dry cleaning technology using a conventional laser has a problem in that it is difficult to simultaneously remove organic and inorganic contaminants on the surface of the workpiece.
In order to solve the above problem, the present inventors have developed a dry cleaning technology for removing organic and inorganic contaminants on a surface of a workpiece with two kinds of laser beams. Such technologies are disclosed in Korean Patent No. 463212 and U.S. Patent Publication No. 2002/0170892, entitled Dry Surface Cleaning Apparatus Using a Laser, filed Mar. 12, 2002. In the above disclosed documents, two kinds of laser beams are used, wherein one of them generates a laser induced shock wave using a focusing lens in the atmosphere, and the other has a characteristic of a short wavelength and is directly radiated to a workpiece to clean it.
At this time, the laser induced shock wave obtained by the one laser beam effectively removes particle-shaped inorganic contaminants existing on a surface of a workpiece, while the direct irradiation of the other laser beam with a short wavelength effectively removes particle-shaped organic contaminants existing on a surface of a workpiece. Consequently, the prior art has an advantage in that all inorganic and organic contaminants, which may exist on a workpiece to be cleaned, can be cleaned by the two kinds of laser beams with different purposes.
However, the prior art has a drawback in that two kinds of laser beams with different purposes should be used to remove inorganic and organic contaminants existing on a surface of a workpiece and a high energy pulse laser should be used for the above two kinds of laser beams which causes an economical loss. Further, in the prior art, a method for generating two kinds of laser beams with different purposes in one laser is suggested. However, since the two kinds of laser beams with different purposes cannot be generated simultaneously, the laser beams are inevitably used in order, and thus, the time required for cleaning process is largely extended.